The present invention concerns a device for damping vibration in a cable. It has particular but not exclusive application in the field of civil engineering works with a structure using such cables, for example suspension or cable-stayed bridges.
These cables or stays are subjected to vibration caused by the wind and/or the rain or else by vehicle traffic on the bridge.
The invention concerns more exactly a device including a first member surrounding and secured to a section of the cable, a second member, connected to an element to which a cable portion is attached, and arranged around the first member, and damping means arranged between the first and second members.
A device of this type, for damping vibration in a stay, is described in European patent 0 343 054. In the damping device presented in this document, the two members delimit a ring-shaped cavity filled with a viscous substance providing the required damping during relative motions of the two members.
This former device has good performance in terms of damping. It has the further advantage of being relatively compact and of not being detrimental to the aesthetic quality of the structure. However, ensuring a seal between the ring-shaped cavity and the exterior can be tricky. A set of joints has to be set in place, which limits the reliability of the device and complicates its installation. On the other hand, the development of a particular device requires a special design of the two members and appropriate sealing means, with this design having to be re-conceived each time, for example, that changes are made to the stay dimensions or to the required dynamic properties.
One object of the present invention is to propose a damping device for a tensioned cable, as a straightforward and reliable response to problems of sealing, the achievement of which is facilitated.
The invention thus proposes a damping device of the type mentioned in the introduction, in which damping means include on the one hand a resilient or visco-elastic ring engaging the first member and the second member, on the other hand a flexible container containing a viscous substance, this flexible container being housed in a ring-shaped compartment formed between the first and second members.
The flexible container constitutes a constant volume damping chamber which can be easily sealed. Cable vibration is effectively attenuated through the combined effect of the resilient or visco-elastic ring and the viscous damping provided by the substance contained in the flexible container. Dissipation of vibrational energy results from the movements of the viscous substance in the flexible container, prompted when the cable vibrates relative to the element to which it is attached.
In a preferred version, the flexible container consists of a hose coiled in the ring-shaped compartment. It is thus possible to adapt to different dimensions of the cable or stay to be damped, simply by adjusting the length of the hose.
To facilitate the installation of the device, the resilient or visco-elastic ring may be composed of two parts of generally semi-cylindrical shape which can be attached to each other by means of pins approximately parallel to the cable section, of assembly bolts or else of a tightening belt.
To advantage, each of these parts comprises several metal half-bushings sunk into a resilient or moulded visco-elastic material, the half-bushing ends protruding from the moulded material and being provided respectively with assembly means such as pinning apertures.
In a version of this latter type, each of the parts comprises two outer half-bushings of the same diameter, located on either side, an inner half-bushing of smaller diameter relative to the cable section direction. It is then the flexibility of the resilient or visco-elastic material between the inner half-bushing and the outer half-bushings which enables the relative motion of the cable section relative to the second member, while exerting return force towards the normal position.